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44 Handbook on the Physics and Chemistry of Rare Earths 4.2.1.3 La3Si6N11:Ce3+ Phosphors La3Si6N11:Ce3+ is one of the recently synthesized yellow-emitting nitride phosphors excitable by blue LEDs (George et al., 2013; Seto et al., 2009; Suehiro et al., 2011). The detailed crystallographic data of La3Si6N11 are reported by Yamane et al. (2014) and show isostructurality with R3Si6N11 (R1⁄4Ce, Pr, Nd, and Sm) (Gaude et al., 1983; Lauterbach and Schnick, 2000; Schlieper and Schnick, 1995, 1996; Woike and Jeitschko, 1995). Ln3Si6N11 has a tetragonal lattice with space group P4bm (no. 100), a 1⁄4 1.0189 nm, c 1⁄4 0.4837 nm, and V 1⁄4 0.5022 nm3 (Woike and Jeitschko, 1995; Yamane et al., 2014). Both La3+ and Si4+ ions occupy two crystallo- graphically independent sites (Fig. 41). La1 and La2 are located at the 4c and 2a sites, respectively, while Si1 and Si2 are located at 8d and 4c sites, respec- tively. The SiN4 tetrahedra form two types of rings, Si4N4 and Si8N8; La1 is surrounded by the Si4N4 ring while La2 is captured in the Si8N8 ring. Both La ions have eightfold nitrogen coordination. The SiN4 tetrahedra are corner sharing each other, providing a 3D network. Three broad bands with maxima at 350, 385, and 455 nm are observed in the excitation spectrum of La3Si6N11:Ce3+ (Fig. 42). Because there are two independent sites available for Ce3+, the bands are attributable to the transi- tions from 4f1 (2F5/2) ground states of Ce3+ to various 5d crystal-field levels defined by the chemical environments around Ce3+ (Seto et al., 2009; Suehiro et al., 2011). The emission spectrum shows an asymmetric broad FIG. 41 a 0.2650(3) 0.2644(3) Crystal structure of La3Si6N11. The unit of bond distance is nm. Pictures were drawn based on the structure data obtained from the database (ICSD #401679). La1 site 0.2551(3) 0.2674(3) 0.2853(3) 0.26227(7) La2 site 0.2650(3) 0.2650(3) 0.2644(3) 0.2650(3) 0.2644(3) 0.2644(3) 0.2863(4) SiN4 La2 La1 b 0.2551(3) 0.2674(3) 0.2853(3)PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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